The prior art is generally cognizant of the need to disperse excess heat from molds used in the formation of molded, thermoplastic objects. Molten thermoplastic material is introduced into a mold and allowed to set or cure by cooling. Generally, the mold is cooler than the molten plastic and absorbs the heat that must be removed from the molten thermoplastic before it will set. Consequently, as a series of objects are molded successively, the temperature of the mold tends to increase.
It is generally desirable to maintain the temperature of the mold at a particular level found to be that which allows a plastic object being molded to exhibit the least possible amount of shrinkage and distortion during the setting or curing process. In any event, it is important to maintain the mold at a consistent operating temperature so as to provide for uniformity among the replications of the object being molded. It is also desirable to remove excess heat from the mold promptly after the molding of an object so as to more quickly prepare the mold for a subsequent introduction of molten plastic, thus increasing the efficiency of production possible by use of the mold.
The control of the temperature of a mold by circulating fluids through channels fashioned in the walls of the mold is known in the art. Conventionally, the fluid is heated to the desired ideal operating temperature and then is circulated through the mold before the first injection or "shot" of hot plastic is introduced. The temperature of the mold increases upon the introduction of molten plastic but is restored to the operating temperature by the continued circulation of considerable quantities of fluid, the temperature of which is maintained at the ideal operating temperature. The fluid is required to circulate substantially all the time that the mold is being used in making successive replications of the object molded.